1. Field of the Invention
The present invention relates to an intruder alarm security device of the type which generates a signal such as an audible signal in response to unauthorized entry to a secured area. The device has particular application for use at a window or door comprising a barrier to the secured area.
2. Discussion of the Prior Art
The prior art is replete with alarm devices which are adapted to be used at a door or window barrier to a secured area and which provide an alarm to indicate an unauthorized entry to the secured area through a barrier. The prior art has developed from very early devices wherein an alarm was sounded by the closing of a circuit to a bell and the release of a spring wound motor causing a bell to sound. See, for example, the patents to B. S. Bell (U.S. Pat. No. 828,834) and A. Zukor (U.S. Pat. No. 1,453,058), respectively.
More recently, alarm devices have developed in the prior art that utilize, generally, a container of a pressurized fluid, a signalling device in the form of an air horn, and an actuating mechanism for opening communication between the pressurized fluid and the air horn to sound are audible alarm. These alarm devices include the following representative known U.S. Pat. Nos:
3,325,800 to W. C. Messick PA1 3,451,369 to N. I. Leve et al PA1 3,659,549 to W. Wagner PA1 3,690,286 to K. T. Gantt PA1 3,695,212 to K. T. Gantt PA1 3,804,053 to J. R. Gray et al PA1 4,024,830 to C. P. Fegley et al PA1 4,024,986 to C. R. Fegley et al
The foregoing alarm devices referring to the general teaching, above, are substantially similar and, aside from the Messick, Leve et al and Wagner patents, the patents relate to alarm devices adapted to use with a door and/or window to provide an alarm upon an unauthorized entry.
The Fegley et al ('830) patent which overall is representative of the above patents further describes a handle or trigger element which is adapted to be moved in response to movement of the movable part of a door, window or movement of some other object. Movement results in release of a spring biased actuating member and the actuating member moves a container having a pressurized fluid toward a piercing point. The piercing point punctures a seal of the container to release fluid for flow to the horn.
While the alarm devices known to the art provide the function of sounding a horn to provide an audible signal as a result of an unauthorized entry to a secured area, or to the vending machine of the Messick patent, for example, the alarm devices of the art are relatively complex in construction and they require cords, etc. to connect the handle or trigger element to the window or other object, or an elaborate biasing arrangement for the handle or trigger element in the use of the alarm device with a door. Importantly, however, the alarm devices of the prior art do not provide for operation which may be characterized as "failsafe". By this, it is meant that the prior art devices either may be "teased" operative thereby to prevent a sufficient pressure build-up within the region of the horn over the period of escape of the fluid from the container for a sounding of the alarm or that the sounding of the alarm may be muffled or muted and thereby not discernible by those prepared to hear the signal. Further, the alarm devices of the art do not provide a metering structure which, first, is capable of permitting entrained particulate material from the closure of the container to clear the device and not block the flow and, second, after only a few milliseconds time, to meter the flow of fluid to extend the period over which the signal is sounded.